2GB to 3GB causes instability

I've got my sytem fully stable at the moment (after a rocky road the last week), but I've been trying to add some more ram and not been having much luck. I have 2GB of Kingston HyperX PC2-8500 (ie. 2*1GB sticks) which are in the machine and running stable (not at 1200MHz, but that's another story!). When I try to add another 2 sticks of the same ram, but 2*512MB, I start getting problems.

Could this be some voltage issue? If so, what? Could it simply be a ram issue and the 1GB isn't healthy? I haven't tried booting up with just the 1GB because I don't think Vista would like it very much (or does it scale how much memory it takes by the amount in the machine?). Currently vista uses 850mb just to get up and running. Anyway, why am I having these issues with the extra ram? Any suggestions?

I'm not sure to what extent, but Vista scales its usage to what's available. It will try to guess what you are going to use and cache those resources in RAM. Less of that will go on as you reduce total capacity from 2GB to 1GB. Performance should not slow to a crawl but you may notice more HDD access.

I would test results with just the 1GB at your current mem settings.

Ok, sounds like a good plan. Thanks.